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Discussion Starter #1
Just got a 2021 Defender and have heard very differing responses on what fuel to use. Dealer said 91 and most people on Facebook say they run best on 87. A lot of people say they ran 91 and had issues with performance and starting the machine.
Just trying to get the most info before I get out in the woods and can’t start the thing.
 

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2021 Can-Am 570 Outlander
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I would go with what the manual says to use. You may or may not see a difference in performance with the higher octane. But is it worth what issues it may create and what it might cost to fix those issues if they don’t go away on their own.
 

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We use all 87 with zero issues. On the X3 however that's not a game you want to be playing. Defender is more than fine on 87 but you will get more power with 91. It just retards the timing a little on 87 but still runs perfectly fine.
 

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Where I live they put 10% ethanol in the 87 octane so I run 91 in my 2019 HD8. I run 91 in all my small engines, chainsaws, lawn mowers....No problems so far.
 

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2015 Outlander XMR 650
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In layman's terms, octane rating is the fuel's resistance to detonating/pre-ignition. Higher the number, better it withstands "premature combustification"

Can-am's Rotax motors and engine management software utilize no knock sensors or variable timing, they can not alter the mechanical spark advance/timing, it's fixed, based on cam/crank position sensor reading

There is no benefit or detriment to using regular ole 87 octane in these things, can't be, by make-up/default. Ethanol is a different topic
 
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In CA we have winter gas and summer gas both with Ethanol....unless we run race gas there are almost no viable alternatives. I try and run a tank at a time so I'm not mixing older gas with the new. I also run a top tier mfg like Chevron with additives. So far between the honda I had for 15 years and the Defender no issues with fuel.
 

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FWIW, I recently purchased a 2020 Defender Limited. The dealer advised me to run only 87 octane fuel in it; apparently that's what it's been tuned for.
 

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been running 91 in all my engines for years. I avoid 87 as much as possible. Ethanol is bad if it sits too long in a gas tank.
 

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2021 Defender Limited / 2015 Outlander Max XT 650
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My dealer said 87 is just fine no issues with them coming in with problems pertaining to gas...... and yes 10% ethanol in it.....
 

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Been running 87 with "up to 10% ethanol" in our 2017 HD Max since new with no issues to date. That is all I can get. All grades have ethanol and Rec fuel isn't available near me unfortunately.
 

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Okay I am new to ATV's but have worked on motorcycles professionally for over 20 years. This topic comes up often with the motorcycles and some of it is caused by fuel pump marketing and some from poor information in the manual.

Fuel pump marketing is where the pumps sell you "regular" or "super, premium" don't be a cheapskate for once someone might see you put "regular" in your vehicle and call the social workers on you. Those names are pure marketing. If you look at the octane rating you then need to look at what version of octane rating is being used. This brings us to the manual.

In the US the octane level at our pumps is a average of motor octane and research octane, what is in the manuals for some motorcycles is a different version with only research octane so the number is higher. Ie: 95Ron will often work out to 87-89 Aki . If you look in your manual be sure to find out which they are referring to.

Your dealers if they do engine work should be able to tell you if lower octane fuel is okay based on the compression ratio and the combustion chamber design your engine has. Some old designs will detonate at low compression ratios but modern designs often can handle another full point or two on the same fuel. If in doubt higher is safer.

That said the lowest octane you can safely run is what is "Best" , by best I mean most hp and cleanest burning. It is common in my world to see engines that are running high test and not run particularly hard all carboned up because all the non-burning additives build up over time. On bikes I have seen power loss on the dyno with too high an octane fuel so I am a believer in you use what is needed and no more.

I am new to ATV's so am far from a expert, do your research. But it would seem odd to me a stock motor designed to be used in all parts of the world where you may not have access to premium fuel would be sold as needing premium . If you have a straight up race or sport rig this could be different as at that point they are trying to extract power. Aftermarket high compression pistons also will require a higher octane, how high you need to find out.
 
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